docs: def _decodeTimestamp(byteIter):
      """ Decodes a 7-octet timestamp """
      dateStr = decodeSemiOctets(byteIter, 7)
      timeZoneStr = dateStr[-2:]        
      return datetime.strptime(dateStr[:-2], '%y%m%d%H%M%S').replace(tzinfo=SmsPduTzInfo(timeZoneStr))